V. Geist

In-situ determination of lattice expansion in proton-bombarded GaP single crystals

Abstract The lattice expansion of GaP, irradiated by 0.3–1.4 MeV protons at 140–715 K was studied in situ by means of the proton- induced Kossel effect. The measurements characterize the surface layer of the crystal with a thickness of 1–2μm. The increase of interplanar spacing Δd{111} measured at T ≥ RT follows a “sublinear” dose-relation with saturation at higher doses. The different initial slopes of the curves obtained at various incidence energies can be described by the energy dependence of the elastic displacement cross section. Measurements performed at T < RT exhibit a more linear “expansion-dose” dependence with a higher expansion rate. As shown by channeling backscattering analysis at RT, the damage density increases with the proton dose in the same manner as the lattice expansion. The expansion was also investigated using X-ray topographs and electron-induced Kossel patterns, confirming the in-situ results.

Recording of Kossel patterns using monochromatic synchrotron radiation

Abstract First results of Kossel measurements using monochromatic synchrotron radiation at the beam line F1 at the synchrotron source HASYLAB/DESY are presented. Methodical aspects of the application of the Kossel technique to specimens sensitive to particle irradiation or covered by layers were surveyed. Furthermore the influence of the selective excitation of characteristic radiation on the background reduction in the case of compound crystals was investigated. Both the excitation of Kossel interferences of a glass covered cuprite sample and an irradiation sensitive synthetic chalcanthite crystal as well as the selective excitation of Ga Kα radiation of a GaAs single crystal were demonstrated. In all cases Kossel photographs rich in contrast could be obtained.

Laue and Kossel diffraction on quasicrystals by means of synchrotron radiation.

Laue experiments using synchrotron radiation have been carried out on quasicrystalline samples mainly with decagonal symmetry. Apart from Laue spots, Kossel lines and diffuse scattering have been observed on the X-ray film simultaneously. High spatial resolution was achieved by the positioning of the X-ray film at a distance of about 350 mm from the sample. Conclusions about the real structure and the crystal quality could be drawn using information obtained from the appearance of the Kossel lines, and the shape and the splitting of the Laue spots, respectively. The dimensions of the mosaic blocks and their tilting behaviour for one of the samples under investigation have been determined.

A simultaneous study of lattice expansion and swelling in proton-bombarded gap single crystals

Abstract The swelling and the lattice expansion of proton bombarded GaP single crystals are simultaneously measured for different proton doses by the “Talystep” method and by the Kossel technique, resp. The results reveal good agreement between the increase in interplanar spacing and the volume change in the damaged region